I have a dataframe with stock returns in one column, strategy values in another & and another column called trades with boolean values (True, False).

My desire is to subtract a particular value (tc) from a cell with in the strategy column if the corresponding bolean is True otherwise the cell is left untouched.

This is my code:

data_1['strategy'][data_1['trades']]-= tc

which runs well. However I would have preffered to use the method of chaining so as to make my code compact.

data_1.assign(strategy = lambda x: x['strategy'][x['trades']]-= tc)

This code throws an error around the -= saying the SyntaxError: invalid syntax

CodePudding user response：

IIUC, you can mask it:

data_1['strategy'] = data_1['strategy'].mask(data_1['trades'], data_1['strategy']-tc)